Solid supports cross-linking

With triethylbenzylammonium bromide (TEBA) as the catalyst on a macro-porous styrene support cross-linked with 12% of divinylbenzene, the following kinetic rate constants k have been obtained (Table 6). It is noteworthy to observe that the apparatus FB-UM gives a rate constant very close to that of the SR-UM with the advantage of avoiding pulverization of the catalyst. Therefore, the FB-UM apparatus can be proposed for any reaction using a solid catalyst and an ultrasonic source to increase the reactivity with respect to silent conditions. ... 

Geotrichum candidum is a well-known catalyst for asymmetric ketone reductions, and different cell-disintegration methods were used to liberate inuacellular CREDs from these cells. Solid shear (bead milling) proved best. Next, various solid supports were examined for the immobilization of the purified enzyme. The CRED was immobilized on silica with an optimized protein loading of 4 mg/g support. Cross-linking vwth glutaraldehyde rendered the preparation more stable and suitable for use in consecutive batches. This immobilized enzyme was found to be a highly efficient biocatalyst formulation for the production of S(-)-l-(10-naphthyl)ethanol [49]. 

The pore size, the pore-size distribution, and the surface area of organic polymeric supports can be controlled easily during production by precipitation processes that take place during the conversion of liquid microdroplets to solid microbeads. For example, polystyrene beads produced without cross-linked agents or diluent are nonporous or contain very small pores. However, by using bigb divinylbenzene (DVB) concentrations and monomer diluents, polymer beads with wide porosities and pore sizes can be produced, depending on the proportion of DVB and monomer diluent. Control of porosity by means of monomer diluent has been extensively studied for polystyrene (3-6) and polymethacrylate (7-10). 

When the polymer was prepared by the suspension polymerization technique, the product was crosslinked beads of unusually uniform size (see Fig. 16 for SEM picture of the beads) with hydrophobic surface characteristics. This shows that cardanyl acrylate/methacry-late can be used as comonomers-cum-cross-linking agents in vinyl polymerizations. This further gives rise to more opportunities to prepare polymer supports for synthesis particularly for experiments in solid-state peptide synthesis. Polymer supports based on activated acrylates have recently been reported to be useful in supported organic reactions, metal ion separation, etc. [198,199]. Copolymers are expected to give better performance and, hence, coplymers of CA and CM A with methyl methacrylate (MMA), styrene (St), and acrylonitrile (AN) were prepared and characterized [196,197]. 

In addition to the insoluble polymers described above, soluble polymers, such as non-cross-linked PS and PEG have proven useful for synthetic applications. However, since synthesis on soluble supports is more difficult to automate, these polymers are not used as extensively as insoluble beads. Soluble polymers offer most of the advantages of both homogeneous-phase chemistry (lack of diffusion phenomena and easy monitoring) and solid-phase techniques (use of excess reagents and ease of isolation and purification of products). Separation of the functionalized matrix is achieved by either precipitation (solvent or heat), membrane filtration, or size-exclusion chromatography [98,99]. 

Immobilization by chemical bonding gives strong, irreversible attachments to a solid support. The bonds are normally covalent but they can be electrostatic. Typical supports are functionalized glass and ceramic beads and fibers. Enzymes are sometimes cross-linked to form a gel. Occasionally, enz5anes can be flocculated while retaining catalytic activity. 

As anticipated in the introduction, cross-linked polymers swell, to variable extent, when put in contact with liquids. Therefore, the working state of any cross-linked organic pol5uner under solid-liquid conditions, no matter if it is a catalyst, a support or a carrier for solid state S5mthesis, is the swollen state. In macroreticular CFPs swelling does not involve the whole polymeric mass it is... 

Chamoin S, Houldsworth S, Kruse CG, Bakker WI, Snieckus V. The Suzuki-Miyaura cross coupling reactions on solid support. Link to solution phase directed ortho metalation. The Leznoff acetal linker approach to biaryl and heterobiaryl aldehydes. Tetrahedron Lett 1998 39 4179-4182. 

Other hydroxylic solid-phase supports such as cross-linked agarose are similarly activated with CDI or V V -carbonyldi-1,2,4-triazole. The activated matrices can then be smoothly coupled with AT-nucleophiles such as glycine, 6-aminohexanoic acid, diamines, or proteins. 212 ... 

Numerous resin supports are commercially available for solid-phase synthesis and some allow the acquisition of quite reasonable quality spectra of compounds bonded to them - and some don t. The resins to avoid (if you intend trying to monitor your reactions by MAS-NMR) are any that are based purely on cross-linked polystyrene. These are too rigid and afford little or no mobility to any bound compound. These resins are relatively cheap and have high specific loadings but will give very poor spectra even in a MAS probe. We see little point in running spectra of compounds on these resins as the quality of the spectra make them virtually useless - and perhaps worse - potentially misleading. 

The novel concept of synthesizing a molecule while attached to a swollen cross-linked resin bead was introduced and demonstrated by R. B. Merrifield with the solid-phase peptide synthesis method about 20 years ago (1,2). The procedure involves the covalent attachment of an amino-acid residue to the polymer bead followed by the addition of subsequent amino-acid units in a stepwise manner under conditions that do not disrupt the attachment to the support. At the completion of the assembly of the peptide, the product is cleaved from the resin and recovered. The macro-scopically insoluble support provides convenient containment of the desired product so that isolation and purification from soluble co-products in the synthesis can be achieved by simple... 

Collioud, A., Clemence, J.-F., Sanger, M., and Sigrist, H. (1993) Oriented and covalent immobilization of target molecules to solid supports Synthesis and application of a light-activatable and thiol-reactive cross-linking reagent. Bioconjugate Chem. 4, 528-536. 

With a view to producing catalysts that can easily be removed from reaction products, typical phase-transfer catalysts such as onium salts, crown ethers, and cryptands have been immobilized on polymer supports. The use of such catalysts in liquid-liquid and liquid-solid two-phase systems has been described as triphase catalysis (Regen, 1975, 1977). Cinquini et al. (1976) have compared the activities of catalysts consisting of ligands bound to chloromethylated polystyrene cross-linked with 2 or 4% divinylbenzene and having different densities of catalytic sites ([126], [127], [ 132]—[ 135]) in the... 

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